UNDERSTANDING MICROCLIMATES

PURPOSE: To apply basic principles of physical science to observations of nature in winter.

MATERIALS: Suitable winter clothing, camera and print film, notebook or index cards, pencil, felt-tipped marker, old ski or other outdoor magazines (optional). Drawing materials may be substituted.

INTRODUCTION: Comments on nature in winter usually lead to a simple, one word description: cold. To a casual observer, the winter scene may appear to be a frozen, white, unchanging wasteland.

You can illustrate the true dynamic nature of the winter environment by making careful observations of temperature variations and wind patterns:

o Warm spots can be found by locating areas where snow melts first. Frost spots form on the coldest objects outdoors. These nearly opposite categories often occur simultaneously in the winter environment, illustrating various forms of heat exchange (conduction, convection and radiation).

o Snow drifts and snow scours (bare spots) are caused by differences in wind speed. The law of conservation of matter requires that the wind increase its speed whenever it passes through a constricted area (Bernoulli's principle). It also may speed up as it passes around a corner. Faster winds can carry more snow; when the wind slows down it deposits some snow.

In this investigation, you will look closely at small, local variations in the winter environment called microclimates. Using basic principles of physics, you will explain your observations. When you complete this activity, you may never look at winter the same way again!

PREDICTION: Use what you know about the natural and manmade sources of heat in winter, and the prevailing winds in your area, to make a prediction.

1. Where do you think you will find evidence of warm spots and frost spots, snow drifts and snow scours in the winter environment?

PROCEDURE:

A. Photograph or draw as many examples of warm spots, frost spots, snow drifts, and snow scours as possible.

(1) Note date, time of day, location of each picture, and the film exposure number in a notebook or on an index card.

(2) Describe the appearance of each site and the heat transfer mechanism involved.

(3) To identify the developed pictures, put the exposure number on the back using a felt tipped marker.

B. Look through old ski or outdoor magazines for other examples of hot and frost spots, and snow drifts and scours.

C. Separate your pictures into four groups: those representing warm spots, frost spots, snow drifts, and snow scours.

D. Neatly display each picture. Label each with the information from your notebook or index cards. Give a brief description and explanation of what is occurring in the picture.

DISCUSSION:

2. Why are most ski slopes built on the north face of mountains?

3. Why does frost often form on the center of bridges and not on the adjoining road surfaces?

4. Why is frost less likely to form on a cloudy night?

5. At the same above-freezing temperature, more melting will occur on a humid winter day than on a dry one. How is this possible?

6. What are the heat transfer mechanisms that makes cats prefer to sleep on the window sill on a sunny winter day?

7. How does overhanging snow (not icicles) form on roofs?

8. Why does the wind often deposit a snow drift inside the edge of a woods?

9. Why is there often a snow scour in front of a snow fence and deep drifts behind the snow fence?

10. How does the wind cause sand dunes to move? How are fences used to stabilize sand dunes?